[PATCH v5 07/30] xprtrdma: Fix ri_max_segs and the result of ro_maxpages

[Chuck Lever <chuck.lever@xxxxxxxxxx>]

With certain combinations of krb5i/p, MR size, and r/wsize, I/O can
fail with EMSGSIZE. This is because the calculated value of
ri_max_segs (the max number of MRs per RPC) exceeded
RPCRDMA_MAX_HDR_SEGS, which caused Read or Write list encoding to
walk off the end of the transport header.

Once that was addressed, the ro_maxpages result has to be corrected
to account for the number of MRs needed for Reply chunks, which is
2 MRs smaller than a normal Read or Write chunk.

Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
---
 net/sunrpc/xprtrdma/fmr_ops.c   |    7 +++++--
 net/sunrpc/xprtrdma/frwr_ops.c  |    7 +++++--
 net/sunrpc/xprtrdma/transport.c |    6 ++++--
 3 files changed, 14 insertions(+), 6 deletions(-)

diff --git a/net/sunrpc/xprtrdma/fmr_ops.c b/net/sunrpc/xprtrdma/fmr_ops.c
index 7f5632c..dd1e91b 100644
--- a/net/sunrpc/xprtrdma/fmr_ops.c
+++ b/net/sunrpc/xprtrdma/fmr_ops.c
@@ -176,7 +176,10 @@ enum {
 
 	ia->ri_max_segs = max_t(unsigned int, 1, RPCRDMA_MAX_DATA_SEGS /
 				RPCRDMA_MAX_FMR_SGES);
-	ia->ri_max_segs += 2;	/* segments for head and tail buffers */
+	/* Reply chunks require segments for head and tail buffers */
+	ia->ri_max_segs += 2;
+	if (ia->ri_max_segs > RPCRDMA_MAX_HDR_SEGS)
+		ia->ri_max_segs = RPCRDMA_MAX_HDR_SEGS;
 	return 0;
 }
 
@@ -186,7 +189,7 @@ enum {
 fmr_op_maxpages(struct rpcrdma_xprt *r_xprt)
 {
 	return min_t(unsigned int, RPCRDMA_MAX_DATA_SEGS,
-		     RPCRDMA_MAX_HDR_SEGS * RPCRDMA_MAX_FMR_SGES);
+		     (r_xprt->rx_ia.ri_max_segs - 2) * RPCRDMA_MAX_FMR_SGES);
 }
 
 /* Use the ib_map_phys_fmr() verb to register a memory region
diff --git a/net/sunrpc/xprtrdma/frwr_ops.c b/net/sunrpc/xprtrdma/frwr_ops.c
index 27222c0..f587e44 100644
--- a/net/sunrpc/xprtrdma/frwr_ops.c
+++ b/net/sunrpc/xprtrdma/frwr_ops.c
@@ -244,7 +244,10 @@
 
 	ia->ri_max_segs = max_t(unsigned int, 1, RPCRDMA_MAX_DATA_SEGS /
 				ia->ri_max_frwr_depth);
-	ia->ri_max_segs += 2;	/* segments for head and tail buffers */
+	/* Reply chunks require segments for head and tail buffers */
+	ia->ri_max_segs += 2;
+	if (ia->ri_max_segs > RPCRDMA_MAX_HDR_SEGS)
+		ia->ri_max_segs = RPCRDMA_MAX_HDR_SEGS;
 	return 0;
 }
 
@@ -257,7 +260,7 @@
 	struct rpcrdma_ia *ia = &r_xprt->rx_ia;
 
 	return min_t(unsigned int, RPCRDMA_MAX_DATA_SEGS,
-		     RPCRDMA_MAX_HDR_SEGS * ia->ri_max_frwr_depth);
+		     (ia->ri_max_segs - 2) * ia->ri_max_frwr_depth);
 }
 
 static void
diff --git a/net/sunrpc/xprtrdma/transport.c b/net/sunrpc/xprtrdma/transport.c
index 134aae2..d3f26c5 100644
--- a/net/sunrpc/xprtrdma/transport.c
+++ b/net/sunrpc/xprtrdma/transport.c
@@ -703,8 +703,10 @@ void xprt_rdma_close(struct rpc_xprt *xprt)
  *	%-ENOTCONN if the caller should reconnect and call again
  *	%-EAGAIN if the caller should call again
  *	%-ENOBUFS if the caller should call again after a delay
- *	%-EIO if a permanent error occurred and the request was not
- *		sent. Do not try to send this message again.
+ *	%-EMSGSIZE if encoding ran out of buffer space. The request
+ *		was not sent. Do not try to send this message again.
+ *	%-EIO if an I/O error occurred. The request was not sent.
+ *		Do not try to send this message again.
  */
 static int
 xprt_rdma_send_request(struct rpc_rqst *rqst)